2000: Grootegoed, a reserve safety, appeared briefly on special teams in the Penn State opener (he did not make a tackle), but then came down with mononucleosis and was sidelined for the rest of his 2000 freshman season. Because of the early illness, he was allowed to redshirt in 2000, his first year at USC.

2001: Originally a safety, Grootegoed was moved to strongside linebacker in 2001 fall camp and, when he was healthy, the redshirt freshman showed a knack for always being around the ball as the starter. However, he missed 4 games (Oregon and Stanford with a left shoulder sprain suffered against Kansas State and then UCLA and Utah after breaking his right lower leg at California). He started 7 games (San Jose State, Arizona State, Notre Dame, Arizona, Oregon State and California on the strong side and Kansas State on the weak side for an injured Frank Strong). Overall in 2001 while appearing in 8 games (he played briefly at Washington, but did not start), he had 32 tackles, including 8 for losses of 13 yards (with a 4-yard sack), a fumble recovery and 2 deflections. He was named to the 2001 The Sporting News Freshman All-American third team and The Sporting News Freshman All-Pac-10 first team.

He had 9 tackles (1 for a loss) against Kansas State, 7 stops (3 for losses) versus Arizona State, 7 tackles (2 for losses) and recovered a fumble to set up a USC field goal at Notre Dame and 5 stops (with a sack) and a deflection against Oregon State.

2002: Grootegoed started for his second season at strongside linebacker as a sophomore in 2002 and led the Trojans in tackles. Overall in 2002 while starting all 13 games, he had a team-best 81 tackles, including a team-best 16.5 for losses of 81 yards (with a team-high 8 sacks for 54 yards), plus 3 forced fumbles, a fumble recovery, an interception which he returned 49 yards and 4 deflections. He made the 2002 All-Pac-10 first team. He missed 2002 spring practice while recovering from a leg injury he suffered during the 2001 season.

He had 3 tackles against Auburn and Colorado, then 9 (1.5 for a loss) at Kansas State, 5 (3 for a loss) against Oregon State. He then had a team-best 9 tackles (1 for a loss) at Washington State. He had a career-best (and team-high) 11 tackles (2 were sacks) and forced a fumble (on a sack) that he recovered (to set up a TD) against California (he also later recovered an on-side kick). Against Washington, he had 3 tackles (1 for a loss) and an interception (which he returned 49 yards to set up a USC TD). He made a team-best 8 tackles at Oregon (with a deflection), 8 stops (including 3 sacks) and a deflection at Stanford and 5 tackles (with a sack) against Arizona State. He ahd a game-best 8 tackles (1 for a loss) at UCLA and added 3 tackles (2 for losses, with a sack) and a deflection against Notre Dame. Against Iowa in the Orange Bowl, he had a game-best 6 tackles (including a 13-yard sack) and forced 2 fumbles (USC recovered 1 to set up a field goal).

2003: Grootegoed started for his third season at strongside linebacker as a junior in 2003. But he sprained his left ankle against Stanford, played briefly against Notre Dame before respraining it, then missed USC's next 4 games of 2003 before seeing brief action against Oregon State (while starting) and Michigan. Overall in 2003 while appearing in 9 games (starting 8), he had 41 tackles, including 4.5 for losses of 24 yards (with 1.5 sacks for 12 yards), plus 1 deflection, 1 fumble recovery and 2 forced fumbles. He was 1 of 11 semifinalists for the 2003 Butkus Award (the only Pac-10 selection) and 1 of 12 semifinalists for the 2003 Lombardi Award. He was named to the 2003 All-Pac-10 second team. He had 5 tackles and forced a fumble (setting up a USC field goal) at Auburn, added 9 stops, a fumble recovery (which set up a USC TD) and a deflection against BYU and then had 4 tackles and a forced fumble (to set up a USC TD) against Hawaii. He made 8 tackles at California, 9 at Arizona State (with 2 for loses) and 4 against Stanford. He had 1 tackle in brief action against both Notre Dame and Michigan.

2004: Grootegoed, an All-American candidate who has uncanny football instincts and can usually be found at the point of action, returns for his fourth season as a starting linebacker as a senior in 2004. After spending the past 3 years on the strong side, he moved to the weak side in 2004 spring practice.